1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine and, particularly, to a fuel injector for an internal combustion engine having a slit-like injection hole to produce a spray of a flat fan shape.
2. Description of the Related Art
In a fuel injector for supplying fuel to an internal combustion engine, the injection hole is made slit-like to produce a spray of a flat fan shape. Japanese Unexamined Patent Publication No. 3-78562 discloses such a fuel injector for an internal combustion engine. The spray of a flat fan shape formed by the fuel injected from the slit-like injection hole of this fuel injector has a small dispersion in concentration and a greatly increased surface area of the spray compared with that of ordinary conical spray, enabling nearly all of the fuel to come into sufficient contact with the air and, hence, to be quickly atomized and mixed. This makes it possible to supply, to the internal combustion engine, a fuel spray in which the fuel is sufficiently atomized and which has a small dispersion in concentration.
FIG. 14 is an enlarged sectional view illustrating the vicinity of an injection hole of a conventional fuel injector for an internal combustion engine, wherein reference numeral 7a denotes a valve body, 7b denotes a fuel reservoir of a hemispherical shape communicated with the injection hole 8, and 7c denotes a nozzle seat portion which can be closed by the valve body 7a. An opening on the outer side of the injection hole 8 at the downstream end in a direction in which the fuel is injected, is made flat and has the shape of a nearly rectangular slit. The injection hole 8 has nearly a fan shape of which the width is gradually narrowed inward, i.e., gradually narrowed toward the upstream side in the direction in which the fuel is injected, so that the fuel can be injected at a predetermined angle in the direction of width. Here, the injection hole 8, the valve body 7a, and the fuel reservoir 7b are formed such that their center axes are on a center axis (C) of the fuel injection valve 7. However, an error in the formed position can occur. For example, FIG. 15 illustrates a state where the injection hole 8 is formed to deviate leftward in the direction of width of the injection hole 8 with respect to the center axis (C) of the fuel injection valve 7, i.e., the state where the injection hole 8 is formed to deviate leftward by an amount of deviation S. Here, symbol (C') denotes the center axis of the injection hole 8.
Referring to FIG. 14, when the center of the fuel reservoir 7b corresponds to the center of the injection hole 8, the fuel flows F1 along the wall surface of the fuel reservoir 7b on the right side and on the left side of the injection hole 8 become symmetrical, and thus the fuel flows symmetrically into the injection hole 8. As described above, furthermore, the fuel reservoir 7b has a hemispherical shape. With the wall surface of the fuel reservoir 7b being shaped as a spherical surface, the fuel flow F1 heading into the injection hole 8 is tilted and possesses velocity components oriented in the direction of width in the injection hole 8. Thus, the fuel is uniformly distributed in the injection hole 8, and is favorably sprayed in compliance with the shape of the injection hole.
Referring to FIG. 15, on the other hand, when the injection hole 8 is deviated in the direction of width and the center of the fuel reservoir 7b does not correspond to the center of the injection hole 8, the fuel flow F2 along the wall surface on the left side of the fuel reservoir 7b and the fuel flow F3 along the wall surface on the right side become asymmetrical with respect to the injection hole 8. That is, the flow-in angle differs depending on the right side and the left side in the injection hole 8. Accordingly, the flow of fuel loses symmetry in the injection hole 8, the fuel is unevenly distributed in the injection hole 8, and the fuel is not sprayed in compliance with the shape of the injection hole. When the spray of a flat fan shape is formed by the slit-like injection hole, the spray is distributed to have a relatively small thickness in the flattened direction. Therefore, uniformity is required in the fuel flow. When the flow of fuel becomes nonuniform, the shape of the spray is greatly disturbed, and the injected fuel loses uniformity in its distribution. Strictly speaking, furthermore, due to deviation in the position of the injection hole 8 as shown in FIG. 15, the area of the opening facing the fuel reservoir 7b in the injection hole 8 undergoes a change, and the flow rate of the fuel is deviated from a preset value, making it difficult to supply the fuel in a desired amount.